Changelog:
0.3.5 -> 0.4
* All GTK_SIGNAL_FUNC instances were replaced by G_CALLBACK.
* The file dialog now uses the GtkFileChooser widget.
* All selections have been changed from GtkCombo to GtkComboBoxEntry.
* The user can now specify the SMTP port (defaults to 25).
* The remaining code was cleaned up (file.c and user_prefs.c).